Common Rail Injector

ABSTRACT

A common rail injector having an injector housing that has a fuel inlet, which communicates with a central high-pressure fuel source outside the injector housing and with a pressure chamber inside the injector housing, from the latter of which, depending on the pressure in a control chamber, highly pressurized fuel is injected into a combustion chamber of an internal combustion engine when a nozzle needle lifts away from its seat, and in which the pressure in the control chamber is directly controlled by a piezoelectric actuator. The end of the nozzle needle oriented away from the combustion chamber accommodates a control chamber delimiting sleeve that can move back and forth and reduce the size of the control chamber-pressurized end surface of the nozzle needle oriented away from the combustion chamber.

The invention relates to a common rail injector having an injectorhousing that has a fuel inlet, which communicates with a centralhigh-pressure fuel source outside the injector housing and with apressure chamber inside the injector housing, from the latter of which,depending on the pressure in a control chamber, highly pressurized fuelis injected into a combustion chamber of an internal combustion enginewhen a nozzle needle lifts away from its seat, and in which the pressurein the control chamber is directly controlled by an actuator, inparticular a piezoelectric actuator.

If the pressure in the control chamber is directly controlled by adeformation of the actuator, in particular a piezoelectric actuator,then this is also referred to as direct nozzle needle control.Conventional common rail injectors with direct nozzle needle controlrequire a relatively large amount of space, particularly in length.

The object of the present invention is to create a common rail injectorhaving an injector housing that has a fuel inlet, which communicateswith a central high-pressure fuel source outside the injector housingand with a pressure chamber inside the injector housing, from the latterof which, depending on the pressure in a control chamber, highlypressurized fuel is injected into a combustion chamber of an internalcombustion engine when a nozzle needle lifts away from its seat, and inwhich the pressure in the control chamber is directly controlled by anactuator, in particular a piezoelectric actuator, which injectorrequires less space, particularly in length, than conventionalinjectors.

DISCLOSURE OF THE INVENTION

In a common rail injector having an injector housing that has a fuelinlet, which communicates with a central high-pressure fuel sourceoutside the injector housing and with a pressure chamber inside theinjector housing, from the latter of which, depending on the pressure ina control chamber, highly pressurized fuel is injected into a combustionchamber of an internal combustion engine when a nozzle needle lifts awayfrom its seat, and in which the pressure in the control chamber isdirectly controlled by an actuator, in particular a piezoelectricactuator, the object of the invention is attained by having the end ofthe nozzle needle oriented away from the combustion chamber accommodatea control chamber delimiting sleeve that can move back and forth andreduce the size of the control chamber-pressurized end surface of thenozzle needle oriented away from the combustion chamber. In the contextof the present invention, a direct control of the pressure in thecontrol chamber is understood to be the generation of a pressure dropand/or a pressure increase due to a volume change of the actuator. Inorder to enable such a direct control, the control chamber is able tocommunicate with an actuator chamber that is delimited by an end surfaceof the actuator or an actuator tip coupled or attached to the actuator.The control chamber delimiting sleeve artificially reduces the size ofthe control chamber. For this reason, the pressure difference in thecontrol chamber required to open and close the nozzle needle can now belower than in conventional injectors with inverse control. This offersthe advantage of permitting shorter actuators to be used.

A preferred exemplary embodiment of the injector is characterized inthat the outer diameter of the control chamber delimiting sleeve issmaller than the outer diameter of the nozzle needle in the region ofits seat. As a result of this, the pressurized surface of the nozzleneedle situated in the control chamber can be designed to be onlyslightly larger than the pressurized surface of the nozzle needleoriented in the opposite direction.

Another preferred exemplary embodiment of the injector is characterizedin that a biting edge is provided on the radial outside of the end ofthe control chamber delimiting sleeve oriented away from the combustionchamber. The biting edge comes to rest in a sealed fashion against theinjector housing in order to delimit the control chamber on the radialinside.

Another preferred exemplary embodiment of the injector is characterizedin that the control chamber delimiting sleeve has a central throughopening that communicates with a leakage oil line let into the injectorhousing. The leakage oil line can serve to drain leakage oil that hasseeped into the interior of the control chamber delimiting sleeve. Inaddition, the leakage oil line relieves the pressure on the interior ofthe control chamber delimiting sleeve.

Another preferred exemplary embodiment of the injector is characterizedin that the end of the nozzle needle oriented away from the combustionchamber has a blind hole let into it, which has a guide section in whichthe control chamber delimiting sleeve is guided in a sealed fashion.This makes it possible for the nozzle needle to move without the controlchamber delimiting sleeve moving along with it.

Another preferred exemplary embodiment of the injector is characterizedin that the blind hole contains a prestressing spring for the controlchamber delimiting sleeve. The prestressing spring serves to keep thecontrol chamber delimiting sleeve in contact with the injector housingwhen the nozzle needle is resting against its seat.

Another preferred exemplary embodiment of the injector is characterizedin that the control chamber is delimited toward the radial outside by anadditional control chamber delimiting sleeve, which is guided so that itcan move back and forth at the end of the nozzle needle oriented awayfrom the combustion chamber. The control chamber delimited by the twocontrol chamber delimiting sleeves is embodied in the form of an annularchamber that is delimited in the axial direction by the injector housingand the end surface of the nozzle needle oriented away from thecombustion chamber.

Another preferred exemplary embodiment of the injector is characterizedin that the control chamber communicates with an actuator pressurechamber that a piezoelectric actuator delimits inside the injectorhousing. Preferably, the piezoelectric actuator is continuously suppliedwith current so that the nozzle needle is situated in the closedposition. When the piezoelectric actuator is deactivated, then thepressure decreases in the actuator pressure chamber and in the controlchamber with which it communicates so that the nozzle needle lifts awayfrom its seat and uncovers at least one injection opening through whichhighly pressurized fuel is injected into the combustion chamber. Thistype of control is also referred to as inverse control.

Other advantages, features, and details of the invention ensue from thefollowing description in which an exemplary embodiment is described indetail in conjunction with the drawing.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The accompanying drawing shows a longitudinal section through anexemplary embodiment of a common rail injector according to the presentinvention. The common rail injector has an injector housing labeled as awhole with the reference numeral 1. The injector housing 1 has a nozzlebody 2, the freely extending lower end of which protrudes into thecombustion chamber of the internal combustion engine to be supplied.With its upper end surface oriented away from the combustion chamber,the nozzle body 2 is clamped axially against an intermediate body 3 andan injector body 4 by means of a retaining nut (not shown).

An axial guide bore 6 is let into the nozzle body 2. A nozzle needle 8is guided so that it can move axially in the guide bore 6. At the tip 9of the nozzle needle 8, a sealing edge 10 is provided, which cooperateswith a sealing seat or sealing surface 11, which is provided on thenozzle body 2. When the sealing edge 10 of the tip 9 of the nozzleneedle 8 is resting against the sealing seat 11, then an injectionopening 13 in the nozzle body 2 is closed. When the sealing edge 10 ofthe nozzle needle tip 9 lifts away from its sealing seat 11, then highlypressurized fuel is injected through the injection opening 13—or throughseveral injection openings—into the combustion chamber of the internalcombustion engine.

Extending away from the tip 9, the nozzle needle 8 has a pressurechamber section 15 that is essentially the shape of a circular cylinder.The pressure chamber section 15 is adjoined by a section 16 that widensin the form of a truncated cone. The sections 15 and 16 are situated ina pressure chamber 17 contained in the nozzle body 2. The section 16that widens in the form of a truncated cone is adjoined by anessentially circular, cylindrical guide section 18. The guide section 18is guided so that it can move back and forth in the axial guide bore 6of the nozzle body 2. A flattened area 20—or several flattenedareas—that is/are provided in the guide section achieve(s) a fluidconnection between the pressure chamber 17 and a nozzle spring chamber22 situated at the end of the nozzle body 2 oriented away from thecombustion chamber.

An arrow 21 indicates that highly pressurized fuel is fed into thenozzle spring chamber 22 via an inlet conduit 23, which is let into theintermediate body 3 and communicates with a high-pressure source (notshown). From the nozzle spring chamber 22, the highly pressurized fuelflows past the flattened area 20 and into the pressure chamber 17. Thehigh-pressure fuel source (not shown) is also referred to as a commonrail.

Adjoining the guide section 18, the nozzle needle 8 is provided with acollar 24 that provides a stop for a spring collar 25. The spring collar25 supports one end of a prestressed nozzle spring 27 placed and/orguided radially outside an essentially circular, cylindrical controlsection 29 provided at the end of the nozzle needle 8 oriented away fromthe combustion chamber.

An outer control chamber delimiting sleeve 31 that has a biting edge 32is guided on the control section 29 at the end of the nozzle needle 8oriented away from the combustion chamber. The biting edge 32 of theouter control chamber delimiting sleeve 31 rests against theintermediate body 3.

The end of the nozzle needle 8 oriented away from the combustion chamberhas a central blind hole 33 let into it, which constitutes a receptacle35 for a sealing spring 36. Toward the end of the nozzle needle 8oriented away from the combustion chamber, the blind hole 33 transitionsinto a guide section 37 in which an inner control chamber delimitingsleeve 38 is guided so that it can move back and forth. The innercontrol chamber delimiting sleeve 38 has an outer diameter 40 that isslightly smaller than the outer diameter 12 of the sealing edge 10 atthe tip 9 of the nozzle needle 8.

The end of the inner control chamber delimiting sleeve 38 oriented awayfrom the combustion chamber is provided with a biting edge 41 with whichthe inner control chamber delimiting sleeve 38 rests against theintermediate body 3. The inner control chamber delimiting sleeve 38 hasa central through opening 43 that communicates with a leakage oilconnecting line 45 that is provided in the intermediate body 3 and,inside the surface of the intermediate body 3 delimited by the bitingedge 41, feeds into the inner chamber delimited by the inner controlchamber delimiting sleeve 38. The leakage oil connecting line 45 in theintermediate body 3 continues on in the form of a leakage oil line 46 inthe injector body 4.

The inner control chamber delimiting sleeve 38 and the outer controlchamber delimiting sleeve 31 radially delimit a control chamber 50 thatis axially delimited by the intermediate body 3 and the end surface ofthe nozzle needle 8 oriented away from the combustion chamber. Thecontrol chamber 50 is embodied in the form of an annular chamber, which,via control chamber connecting lines 52 and 53 provided in theintermediate body 3, communicates with an actuator pressure chambercontained in the injector body 4. The actuator pressure chamber 55 isdelimited in the axial direction by an actuator 56 at the end orientedaway from the combustion chamber and by the intermediate body 3 at theend oriented toward the combustion chamber. Toward the radial outside,the actuator pressure chamber 55 is delimited by an actuator sleeve 58.The actuator pressure chamber 55 communicates via connecting lines (notshown) with the inlet conduit 23 so that the actuator pressure chamber55 is filled with highly pressurized fuel. The actuator sleeve 58 isprovided with a biting edge 57 that rests against the intermediate body3. The opposite end of the actuator sleeve 58 is acted on by an actuatorspring 59 that keeps the biting edge 57 of the actuator sleeve 58 incontact with the intermediate body 3.

The actuator 56 is a piezoelectric actuator that has a larger volumewhen supplied with current than when it is without current. A doublearrow 60 indicates that the actuator 56 can deform, increasing ordecreasing the pressure in the actuator pressure chamber 55 and thecontrol chamber 50 with which it communicates.

When the actuator, which is otherwise continuously supplied withcurrent, is deactivated, then this decreases the pressure in theactuator pressure chamber 55 and the control chamber 50 with which itcommunicates. The pressurized surfaces of the nozzle needle 8 aredesigned so that this pressure drop causes the sealing edge 10 of thenozzle needle 8 to lift away from the sealing seat 11 so that highlypressurized fuel from the pressure chamber 17 is injected through theinjection opening of 13 into the combustion chamber of the internalcombustion engine.

The gas back pressure of the combustion chamber acts on the region ofthe nozzle needle underneath the sealing edge 10. The high pressuresupplied via the inlet conduit 23, which is also referred to as commonrail pressure, acts on the region of the nozzle needle 8 above thesealing edge 10. If the nozzle is to be opened, then a force equilibriumin the region of the control chamber 50 must be achieved in relation tothe common rail pressure acting on the diameter 12. In order to lift thenozzle needle 8, the pressure in the control chamber 50 is decreasedwith the aid of the actuator 56.

The use of the inner control chamber delimiting sleeve 38 is able toartificially reduce the size of the control chamber 50 since leakage oilpressure prevails on the interior of the inner control chamberdelimiting sleeve 38. The diameter 40 of the inner control chamberdelimiting sleeve 38 is preferably designed so that it is smaller thanthe diameter 12 of the sealing edge 10 of the nozzle needle 8. In thedesign process, care must be taken that the sum of the forces in theregion of the sealing seat 11 is less than the force that results fromthe compressive forces acting in the control chamber 50 and the springforces of the nozzle spring 27 and the sealing spring 36.

1-8. (canceled)
 9. In a common rail injector having an injector housingthat has a fuel inlet, which communicates with a central high-pressurefuel source outside the injector housing and with a pressure chamberinside the injector housing, from the latter of which, depending on thepressure in a control chamber, highly pressurized fuel is injected intoa combustion chamber of an internal combustion engine when a nozzleneedle lifts away from its seat, and in which the pressure in thecontrol chamber is directly controlled by a piezoelectric actuator, theimprovement wherein the end of the nozzle needle oriented away from thecombustion chamber accommodates a control chamber delimiting sleevemounted for movement back and forth to reduce the size of the controlchamber-pressurized end surface of the nozzle needle oriented away fromthe combustion chamber.
 10. The common rail injector according to claim9, wherein the outer diameter of the control chamber delimiting sleeveis smaller than the outer diameter of the nozzle needle in the region ofits seat.
 11. The common rail injector according to claim 9, wherein thecontrol chamber delimiting sleeve comprises a biting edge on its radialoutside at the end oriented away from the combustion chamber.
 12. Thecommon rail injector according to claim 10, wherein the control chamberdelimiting sleeve comprises a biting edge on its radial outside at theend oriented away from the combustion chamber.
 13. The common railinjector according to claim 11, wherein the control chamber delimitingsleeve comprises a central through hole that communicates with a leakageoil line that is let into the injector housing.
 14. The common railinjector according to claim 12, wherein the control chamber delimitingsleeve comprises a central through hole that communicates with a leakageoil line that is let into the injector housing.
 15. The common railinjector according to claim 9, further comprising a blind hole let intothe end of the nozzle needle oriented away from the combustion chamber,which blind hole has a guide section in which the control chamberdelimiting sleeve is guided in a sealed fashion.
 16. The common railinjector according to claim 10, further comprising a blind hole let intothe end of the nozzle needle oriented away from the combustion chamber,which blind hole has a guide section in which the control chamberdelimiting sleeve is guided in a sealed fashion.
 17. The common railinjector according to claim 11, further comprising a blind hole let intothe end of the nozzle needle oriented away from the combustion chamber,which blind hole has a guide section in which the control chamberdelimiting sleeve is guided in a sealed fashion.
 18. The common railinjector according to claim 13, further comprising a blind hole let intothe end of the nozzle needle oriented away from the combustion chamber,which blind hole has a guide section in which the control chamberdelimiting sleeve is guided in a sealed fashion.
 19. The common railinjector according to claim 13, further comprises a prestressing springin the blind hole in the nozzle needle for the control chamberdelimiting sleeve.
 20. The common rail injector according to claim 11,further comprises a prestressing spring in the blind hole in the nozzleneedle for the control chamber delimiting sleeve.